Top tensioned riser adaptor

ABSTRACT

An adaptor for a top tensioned riser that allows the riser to be tied in with wellheads beyond the normal range of the top tensioned riser. An adaptor spool attaches between the top tensioned riser and the subsea wellhead. An adaptor spool hanger may land in the adaptor spool. The adaptor spool is provided with a side penetration to which a flow line may be connected. The flow line is provided with a connector that connects to a production line from a remote location. This allows the fluid production to flow from the remote location through the existing top tensioned riser to the host facility. The tieback connector/stress joint may also be provided with a flow line prepared to accept remote field tiebacks, which are also piggable.

RELATED APPLICATIONS

This application references and claims the benefit of ProvisionalApplication Ser. No. 60/689,846 filed on Jun. 13, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is generally related to production risers used on offshorestructures and more particularly to top tensioned risers.

2. General Background

In the offshore production of oil and gas (fluids), offshore hostfacilities can be one of many different types, such as TLP's (tensionleg platforms), Mini-TLP's, Spars, Semi-submersibles, etc. These hostfacilities most often bring production fluid onboard and produce thefluid for export through a pipeline. The fluid comes from subsea wellseither directly to the host facility or via manifolds that commingle theproduction fluid from several different wells, prior to the fluids beingbrought onboard a host facility.

The means typically used to bring the production fluids to the hostfacility include steel catenary risers (SCR's), flexible flowlines, toptensioned risers (TTR's), and free standing risers.

Steel catenary risers (SCR's) are essentially a pipeline that hangs offof the host facility by way of either a hang-off porch and flex joint orpull tube and stress joint. Installation involves a lay barge, whichdrives up installation costs, as field welding is required tomanufacture the SCR. The weight of the SCR imparts a high hang off loadonto the host facility. There are also fatigue issues associated withhost facility motions being transmitted into the SCR.

Flexible flowlines are a multi-layer flexible hose that hang off thehost facility via a collar. The hoses hang in a catenary shape similarto an SCR but with a more dramatic sag. The flexible flowline offers thebenefit of faster installation times relative to the SCR, as there areno in-field welds that must be made. Typically, the flexible flowline isreeled out during installation. The flexible flowline can also reducethe payload imparted onto the host facility, as the departure angles forflexible flowlines are smaller than SCR's, which yield a shorter freehanging catenary length, reducing the weight, which is another benefit.However, multiple layers are required to produce the flexible flowlineswhich typically cause the weight per foot to be higher than the SCR.Weight must be considered in a case by case basis. Flexible flowlinesare expensive to manufacture relative to pipe. Not only is themanufacturing cost high, but the flexible flowlines have temperature andpressure limitations relative to steel pipe.

Another alternative is a top tensioned riser (TTR). These risers aremade of steel pipe with specialty joints located at the sea floor andthe keel of the host facility. These specialty joints help reducelocalized high bending loads generated in these areas. The weight of theTTR is either supported by the host facility or via air cans thatprovide buoyancy independent of the host facility. Installation of thetop tensioned riser is accomplished via a rig located on top of the hostfacility. The subsea wellhead that a TTR is tying back to must belocated within a relatively small distance from the well slot where theTTR enters the host facility. This is one of the main restrictions of aTTR.

A free standing riser (FSR) is a combination of a TTR and a flexibleriser. The FSR is a buoyancy can supported TTR that is located outsideof the host facility. Another difference is that the top of the FSR'sair can is located well below the mean water level, approximately fivehundred feet. A flexible flowline is then attached from the top of theFSR to the host facility. This riser concept has several benefits. Hostfacility motions are decoupled from the riser via the flexible flowline.Another benefit is that the payload imparted on the host facility issmall because only approximately one thousand feet of flexible flowlineis hanging from the host facility.

It can be seen that TTR's have some disadvantages. For example, if thewells that the TTR's are producing from have their production depletebefore the design life of the riser is up, the TTR cannot readily bemoved to accommodate another wellhead, as described above. Because TTR'shave not been designed to be tied in from wellheads beyond the normalreach of a TTR, the useful life of TTR's can be limited. This results inthe need to have other types of risers, as described above, which addsto the complexity and cost of an offshore host facility.

SUMMARY OF THE INVENTION

The invention addresses the above need. What is provided is an adaptorfor a top tensioned riser that allows the riser to be tied in withwellheads that are beyond the normal range of the top tensioned riser.An adaptor spool attaches between the top tensioned riser and the subseawellhead. An adaptor spool hanger may land in the adaptor spool. Theadaptor spool is provided with a side penetration to which a flow linemay be connected. The side penetration is provided with a flow lineconnector hub that accepts a flowline connector from a remote wellproduction line. This allows the production fluid to flow from theremote well through the existing top tensioned riser to the host. Thetieback connector/stress joint may also be provided with a sidepenetration if the project anticipates the TTR being used for remotetiebacks in the future.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention reference should be made to the following description, takenin conjunction with the accompanying drawings in which like parts aregiven like reference numerals, and wherein:

FIG. 1 is a side sectional view of the invention that illustrates theadaptor spool hanger positioned in the adaptor spool.

FIG. 2 is a side sectional view of the invention that illustrates theinvention may be produced for sizes up to the bore size of the TTR. Aswith FIG. 1, this configuration has a piggable bore.

FIG. 3 is a side sectional view of the invention that illustrates anarrangement that allows production from the vertically accessible welland a remote well.

FIG. 3 a is a side sectional view of the invention that illustrates anarrangement with multiple flow lines to receive production fluids frommultiple remote wells and the vertically accessible well.

FIG. 3 b is a side sectional view of the invention that illustrates anarrangement where the flow lines are used for injection into, andproduction from, remote wells.

FIG. 3 c is a side sectional view of the invention that illustrates anarrangement where production from a remote well and the verticallyaccessible well are allowed along with injection into the verticallyaccessible well.

FIG. 3 d is a sectional view taken along lines 3 d-3 d in FIG. 3.

FIG. 3 e is a sectional view taken along lines 3 e-3 e in FIG. 3 a.

FIG. 3 f is a sectional view taken along lines 3 f-3 f in FIG. 3 b.

FIG. 3 g is a sectional view taken along lines 3 g-3 g in FIG. 3 c.

FIG. 4 is a side sectional view of the invention that illustrates anarrangement for injection of fluids into a remote well.

FIG. 5 is a side sectional view of the invention that illustrates anarrangement for production from the vertically accessible well andinjection of fluids through the TTR annulus into a remote well.

FIG. 6 is a side sectional view of the invention that illustrates anarrangement for injection into the vertically accessible well andproduction from a remote well.

FIG. 7 illustrates an alternate embodiment of the invention where theoriginal tieback connector/stress joint is designed according to thegeneral principle of the invention.

FIG. 8 is a side section view that illustrates the remote tieback mayhave a bore size equal to the TTR bore.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, it is seen in FIG. 1 that the invention isgenerally indicated by the numeral 10. The adaptor 10 for the toptensioned riser is generally comprised of an adaptor spool 12 and anadaptor spool hanger 14. The arrangement of the hanger 14 is optionaldepending upon the situation.

Adaptor spool 12 is designed to physically lock to the upper most pieceof the subsea wellhead 16 and so is provided with a connector 18 at thelower end for attachment to the wellhead 16. The upper end of adaptorspool 12 is designed to be connected to the tieback connector 20. Thus,the profile of the upper end of the adaptor spool mandrel 12 duplicatesthe profile of the upper most end of the subsea wellhead 16 and therebyforms a connection for attachment to the tieback connector 20. Thetieback connector 20 is essentially the lower end of the riser 23.

Seals 24 are provided at the upper and lower ends of the adaptor spool12 and are the same design and profiles originally used between thesubsea wellhead 16 and tieback connector 20 since the adaptor spoolprovides the same internal profiles as the original connection betweenthe subsea wellhead 16 and the tieback connector 20. The adaptor spool12 may be designed to be attached to any tieback connector.

A curved bore 26 is provided through the sidewall of the adaptor spool12 to define a flow path. Bore 26 exits the side of adaptor spool 12.Bore 26 turns to parallel the longitudinal axis of adaptor spool 12. Theturn in bore 26 has a radius that is piggable and meets the minimumpigging radii dictated by industry standards.

Flow line connector 28 is provided at bore 26 and designed to receive aflow line 30. The flow line 30 extends away from the adaptor spool 12,wellhead 16, and tieback connector 20 a sufficient distance to allow theconnection of a pipeline, jumper, flexible riser, etc. thereto. Asuitable connection 32 is provided on flow line 30 for this purpose.

It can be seen in FIG. 1 that adaptor spool 12 is provided with alongitudinal bore 34 therethrough to allow the flow of fluids in thenormal manner from the wellhead 16 into the riser 23 when the adaptorspool hanger 14 is not used.

The purpose of the hanger 14 is to divert the tubing bore from the toptensioned riser's vertical orientation to exiting the top tensionedriser system entirely. This requires the hanger to generate a sealbetween its OD (outer diameter) and the ID (inner diameter) of the spacethat it is positioned in inside of the adaptor spool 12. Seals 36 areprovided on the OD of the hanger 14 for this purpose. Fluid can thenflow from a field flow line, through the external flow line 30, throughthe adaptor spool 12, up the tubing string, and into the surface wellhead.

The adaptor spool hanger 14 may be deployed either with the adaptorspool or be independently run or installed into the adaptor spool 12 viaa surface run tubing string or run through the top tensioned riser on atubing string. In the latter case, the adaptor spool hanger 14 wouldhave to be functioned to lock it to either the adaptor spool 12 or thetieback connector 20.

FIG. 2 illustrates an arrangement where the adaptor spool hanger is notused. For bores of this size the flowline connector 28 will most likelynot be used. The horizontal penetration through the adaptor 12 will befabricated as part of the adaptor. There will not be a separateconnection. Bore 26 is provided with a piggable radius in this casealso. This arrangement allows the accommodation of large diameter flowlines. In this arrangement, it is seen that the diameter through theriser 23, adaptor spool 12, and flowline 30 are the same. Pipe 29 isreceived in bore 26. FIG. 2 illustrates a more proper piggable turn inthe invention. The remaining drawings illustrate a different radius turnsimply for ease of illustration but are also intended to provide apiggable radius turn.

FIG. 3 illustrates an arrangement that allows a dual completion throughone top tensioned riser 23. In addition to bore 26, the adaptor spoolhanger 14 is also provided with a through bore 40. Fluid line 42 extendsthrough the bore 40 from a packer 44 in the well head 16 and up throughthe riser 23 for producing fluids from the well. A second fluid line 46in fluid communication with bore 26 extends up through the riser 23 fordelivering production fluids from a remote well through the toptensioned riser 23.

FIG. 3 a illustrates an arrangement similar to FIG. 3 where additionalflow lines 30 are provided in fluid communication with the adaptor spoolhanger 14 through additional bores 26 (seen in FIG. 3 e) to receivefluid production from additional remote wells.

FIG. 3 b illustrates an arrangement where fluid line 46 is used todeliver gas or water to a remote well to assist in production ofhydrocarbons.

FIG. 3 c illustrates an arrangement where fluid line 46 is used toinject water or gas into the well and fluid line 42 is used to producehydrocarbons from the well. Flow line 30 is used as described above toreceive fluids from a remote well.

FIG. 4 illustrates an arrangement where fluid line 46 is used to delivergas or water to a remote well to assist in driving production.

FIG. 5 illustrates an arrangement where water or gas is delivered downthe annulus of the riser 23 while the vertically accessible well isstill producing fluids through fluid line 42. Packer 44 causes the wateror gas to be directed into flow line 30 and to a remote well.

FIG. 6 illustrates an arrangement where the adaptor spool hanger 14 isprovided with a longitudinal bore 48. This allows the injection of wateror gas through the annulus of the riser 23 and into the verticallyaccessible well while still receiving production fluids from a remotewell through flow line 30 and line 46.

FIG. 7 illustrates an arrangement where the original tiebackconnector/stress joint has been designed with the side penetration forremote well tiebacks. Therefore, the tieback connector/stress joint maybe used as it typically is until the vertically accessible well isdepleted, at which time a remote well may be tied back without insertingan adaptor spool. A flowline 30 is either preinstalled onto the tiebackconnector/stress joint or installed via ROV at a later date. The sametype of multiple line arrangements seen in FIG. 3-6 may also be used inthis arrangement with the tieback connector/stress joint. FIG. 8illustrates the large bore piggable radius and an arrangement where theadaptor spool hanger is not used. As with all Figures included hereinthis arrangemtn can be made with a piggable bore.

During installation, the adaptor spool 12 may be deployed from thesurface during the initial top tensioned riser installation, whilererunning of an existing top tensioned riser, or retrofitted into a toptensioned riser that has already been deployed. If the spool is beingdeployed into an existing top tensioned riser, the adaptor spool islowered on a down line, the tieback connector 20 is unlocked, the toptensioned riser is picked up, the adaptor spool is landed and locked tothe subsea wellhead 16, with assistance provided by an ROV (remotelyoperated vehicle), and the top tensioned riser is then landed and lockedto the adaptor spool 12. This makes the adaptor spool 12 part of theexternal barrier to the environment for the top tensioned riser.

The adaptor spool 12 is manufactured in order to meet or exceed all thedesign requirements of the top tensioned riser, i.e. material selection,drift diameter, load requirements, etc. The adaptor spool 12 willgenerate a sealed bore from the upper most piece of subsea wellheadequipment through to the tieback connector 20 on the top tensionedriser. This is accomplished by utilizing the same interface design andinterface profiles originally between the top tensioned riser and thesubsea wellhead, as indicated above.

The connector on the adaptor spool 12 is rated to meet or exceed allglobal loading, fatigue requirements, internal pressures, externalpressures, etc.

The invention provides a number of advantages.

Existing top tensioned risers can have their life extended if the wellsthat the risers are producing from have their production deplete beforethe design life of the riser is up. Installation of the adaptor spool 12and adaptor spool hanger 14 allows production from remote trees throughthe existing top tensioned riser. This allows the operator to produceremote wells in a series or parallel through the same top tensionedriser.

If the top tensioned riser is tensioned from an air can, which isindependent of the host facility, the host facility may take onadditional tiebacks with no additional payload implications. Otherwise,additional slots would either have to be available or planned into theoriginal design.

If a top tensioned riser is still producing, but at a low rate, theoperator can plug the bore of the riser just below the mudline using aplug 38 (seen in FIG. 2), run an adaptor spool 12 and adaptor spoolhanger 14, and bring a high producing satellite well on line. Thevertically accessible well can be brought back on line at a later date.

Fewer or no steel catenary risers (SCR's) could be designed into thehost facility production system, thereby reducing the design criteriafor the entire host facility. The numbers of SCR's and top tensionedrisers could be optimized on a per project basis. This is especiallybeneficial to top tensioned risers that are tensioned by buoyancy cans.

Large diameter flow lines can be accommodated if the verticallyaccessible well is plugged after the tubing is removed from the toptensioned riser. In this case, the diameter through the riser pipe,adaptor spool 12, and flow line to a manifold would be the same. Therewould be no adaptor spool hanger 14 in this case.

A dual completion can be had through one top tensioned riser. Thevertically accessible well can continue to produce while a second tubingstring exits the adaptor spool 12 and adaptor spool hanger 14. In thisinstance, the adaptor spool hanger 14 will have both a longitudinalthrough bore and a radial bore that exits into the adaptor spool 12 asseen in FIG. 3.

Both a production line and gas lift can go out to satellite wellsthrough the adaptor spool 12 and adaptor spool hanger 14.

Multiple completion tubing strings, gas lift lines, and/or waterinjection lines can be run through the same top tensioned riser. Theadaptor spool 12 and adaptor spool hanger 14 will require multipleoutlets in this instance.

The production arrangement can be used for water injection. Thisreverses the normal flow path, sending water down the riser and out to awater injection well. Water injection can be sent straight through thetubing, which exits the adaptor spool 12. Water injection can be sentdown a top tensioned riser annulus while the vertically accessible wellis still producing through the tubing. In this case, the tubing willexit the bottom of the adaptor spool hanger 14 and the top tensionedriser annulus will feed out the penetration into the adaptor spool.Water injection can be sent down the annulus of the top tensioned riserinto the vertically accessible well while production comes through theadaptor spool 12 and adaptor spool hanger 14 from a satellite well.

Both dual and single barrier top tensioned risers can be accommodated bythe invention.

Because many varying and differing embodiments may be made within thescope of the inventive concept herein taught and because manymodifications may be made in the embodiment herein detailed inaccordance with the descriptive requirement of the law, it is to beunderstood that the details herein are to be interpreted as illustrativeand not in a limiting sense.

1. In an offshore production arrangement where a top tensioned riser isconnected to a subsea wellhead by a tieback connector having alongitudinal bore in fluid communication with the subsea wellhead andthe top tensioned riser, an adaptor for the top tensioned riser, saidadaptor comprising: a. an adaptor spool with a longitudinal boretherethrough; and b. a an adaptor spool hanger received in thelongitudinal bore through said adaptor spool.
 2. The adaptor of claim 1,wherein said adaptor spool is received between the riser and thewellhead so as to be in fluid communication with the riser and wellhead.3. The adaptor of claim 1, wherein said adaptor spool hanger includes abore therethrough that exits the side of said adaptor spool hanger andsaid adaptor spool and is in fluid communication with the riser.
 4. Theadaptor of claim 3, wherein the bore through said adaptor spool hangeris piggable.
 5. The adaptor of claim 1, wherein said adaptor spoolhanger includes a bore therethrough that exits the side of said adaptorspool hanger and said adaptor spool and is in fluid communication withthe riser and a longitudinal bore therethrough in fluid communicationwith the wellhead and riser.
 6. In an offshore production arrangementwhere a top tensioned riser is connected to a subsea wellhead by atieback connector having a longitudinal bore in fluid communication withthe subsea wellhead and the top tensioned riser, an adaptor for the toptensioned riser, said adaptor comprising: a. an adaptor spool receivedbetween the wellhead and riser, said adaptor spool having a longitudinalbore therethrough in fluid communication with the riser and wellhead;and b. a an adaptor spool hanger received in the longitudinal borethrough said adaptor spool, said adaptor spool hanger having a piggablebore therethrough that exits the side of said adaptor spool hanger andsaid adaptor spool and is in fluid communication with the riser.
 7. Theadaptor of claim 6, further comprising said adaptor spool having alongitudinal bore therethrough in fluid communication with the riser andwellhead.
 8. In an offshore production arrangement where a top tensionedriser is connected to a subsea wellhead by a tieback connector having alongitudinal bore in fluid communication with the subsea wellhead andthe top tensioned riser, an adaptor for the top tensioned riser, saidadaptor comprising: a. an adaptor spool received between the wellheadand riser, said adaptor spool having a bore that exits the side of saidadaptor spool and is in fluid communication with the riser; and b. aseparate fluid line received in said adaptor spool, the riser, and thewell for producing fluids from the wellhead.
 9. In an offshoreproduction arrangement where a top tensioned riser is connected to asubsea wellhead by a tieback connector having a longitudinal bore influid communication with the subsea wellhead and the top tensionedriser, an adaptor for the top tensioned riser, said adaptor comprisingan adaptor spool received between the wellhead and riser, said adaptorspool having a bore that exits the side of said adaptor spool and is influid communication with the riser.